This invention relates to Fe-Ni alloys with improved punching properties suitable as materials for electron gun parts, such as electrodes for electron guns, and also relates to punched electron gun parts, typically electron gun electrodes, obtained by blanking a stock of such alloy and punching small holes in the blanks for passage of electron beams therethrough.
In FIG. 1 is shown a cross section of a color picture tube of the shadow mask type already known in the art. A panel 1 is coated on the back side with a phosphor film 2 that generates the three primary colors of red, green, and blue. In the neck is housed an electron gun 4 that emits electron beams 3. The electron beams 3 are deflected in scanning by a deflection yoke 5. The numeral 6 indicates a shadow mask and the numeral 7 indicates a magnetic shield.
In FIG. 2, (a) and (b) are perspective and cross sectional views, respectively, of an electrode 10 as an example of a punched part to be fitted in the electron gun 4. The electrode 10 acts to accelerate electrons emitted from a cathode in the electron gun. The electrode has small holes 10a, 10b, and 10c made by coining and punching so as to allow red, green, and blue color-generating beams, respectively, to pass through them.
In general, the electron gun parts for use in picture tubes and the like are completed by blanking and press punching (called hereinafter merely punching), with or without coining, a sheet of nonmagnetic stainless steel about 0.05 to 0.5 mm thick.
As materials commonly used for electron gun parts of picture tubes and the like, nonmagnetic stainless steels are well known. Also in the case of the electrode 10 that accelerates the electrons emitted from the cathode of an electron gun, it has long been desired to have a magnetic permeability, as a measure of nonmagnetism, close to 1. Recently however, more weight has been put on low thermal expansion properties than on the permeability. With the advent of higher refinement, higher performance picture tubes for computer displays and the like in recent years, it has been noted that subtle dimensional changes with thermal expansion of electrode parts influence the picture quality (color purity) on the panel 1 (see FIG. 1). To cope with the situation, Fe-Ni alloys having low-expansion properties, notably Fe-42% Ni alloy (42 alloy), have come into use as electrode materials.
The 42 alloy of the prior art, however, presents a burr formation problem. That is, as electrode blanks of the 42 alloy are punched with a pattern of small holes 10a, 10b, and 10c each, burrs B are formed on the edges 10e of the holes where punches have forced slugs down and cut them off from the blank (see FIG. 2). The burrs that result from the punching have adverse effects upon the dimensional accuracy of electron gun parts that must meet severe precision requirements. Abnormal discharge from the burrs under high voltage sometimes proves fatal to the electron guns due to decreases in withstand voltage. The tendency toward picture tubes of even greater refinement is making the requirement for the reduction of burring from electron gun parts more and more exacting.
Improvements in the punching properties of Fe-Ni alloys have hitherto been proposed, for example, in Japanese Patent Application Kokai Nos. 6-122945, 6-184703, 7-3400, and 7-34199.
Of those proposals, Kokai No. 6-184703 specifies an S content in the range of 0.002 to 0.05% and disperses S or an S compound along grain boundaries or within grains in the alloy stock. However, the mere addition of S, a free-cutting element, in a specified percentage cannot be deemed adequate for the control of burrs in the modern punching working to most precise specifications.
The remaining Kokai Nos. 6-122945, 7-3400, and 7-34199 propose adding such strengthening elements as Ti, Nb, V, Ta, W, or/and Zr to the alloy for imparting increased hardness and proper extent of embrittlement to the alloy to suppress burring. These proposals, however, posed problems of shortened punching die life with increased hardness and of increased cost with the addition of such special elements.
This invention has for its object to settle the aforedescribed problems of the prior art and provide an Fe-Ni alloy for electron gun parts which is improved in punching properties without attendant shortening of die life or additional expenditure on special elements, and also provide punched parts for electron guns, typified by electron gun electrodes, made of the alloy by punching.